Deep hard X-ray source counts from a fluctuation analysis of ASCA SIS images

被引:21
作者
Gendreau, KC [1 ]
Barcons, X
Fabian, AC
机构
[1] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[2] Univ Cantabria, Inst Fis Cantabria, CSIC, E-39005 Santander, Spain
[3] Univ Cambridge, Inst Astron, Cambridge CB3 0HA, England
关键词
methods : statistical; diffuse radiation; X-rays : general;
D O I
10.1046/j.1365-8711.1998.01407.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
An analysis of the spatial fluctuations in 15 deep ASCA SISO images has been conducted in order to probe the 2-10 keV X-ray source counts down to a flux limit similar to 2 x 10(-14) erg cm-2 s(-1). Special care has been taken in modelling the fluctuations in terms of the sensitivity maps of every one of the 16 regions (5.6 x 5.6 arcmin(2) each) into which the SISO has been divided, by means of ray-tracing simulations with improved optical constants in the X-ray telescope. The very extended 'sidelobes' (extending up to a couple of degrees) exhibited by these sensitivity maps make our analysis sensitive to both faint on-axis sources and brighter off-axis ones, the former being dominant. The source counts in the range (2-12) x 10(-14) erg cm(-2) s(-1) are found to be close to a Euclidean form which extrapolates well to previous results from higher fluxes and are in reasonable agreement with some recent ASCA surveys. However, our results disagree with the deep survey counts by Georgantopoulos et al, The possibility that the source counts flatten to a sub-Euclidean form, as is observed at soft energies in ROSAT data, is only weakly constrained to happen at a flux < 1.8 x 10(-12) erg cm(-2) s(-1) (90 per cent confidence). Down to the sensitivity limit of our analysis, the integrated contribution of the sources the imprint of which is seen in the fluctuations amounts to similar to 35 +/- 13 per cent of the extragalactic 2-10 keV X-ray background.
引用
收藏
页码:41 / 48
页数:8
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